1. Field of the Invention
The present invention relates to electromechanical branching filters of the type comprising a mechanical vibration system which is capable of branching an input electrical signal into two output electrical signals having different frequency components or of synthesizing two signals of different frequency components into one output signal. More particularly, the invention relates to an electromechanical branching filter comprising electromechanical, wide and narrow bandpass filters, the passband center frequencies of which are adjacent to each other.
2. Description of the Prior Art
One recent trend in the field of carrier telephone transmission systems has been toward the realization of higher multiplexing ratios which permit economical transmission of a greater number of speech channel signals. This has induced the need for filters of smaller dimensions, such as electromechanical branching filters comprising a plurality of mechanically coupled electromechanical filters. A typical filter of this type is disclosed in the U.S. Pat. No. 2,955,267, entitled "Electromechanical Torsional Band Pass Wave Filter", granted to Warren P. Mason on Oct. 4, 1960. In the Mason arrangement, electromechanical filters having different passbands are linked to a common transducer designed to have a passband wide enough to cover all the passbands of the individual electromechanical filters. In such construction, however, the common transducer operates as an idle element in that it does not directly contribute to attenuation of signal energy, since its passband covers all the various passbands involved.